Method to improve blowthrough and EGR via split exhaust

Abstract

Methods and systems are provided for a boosted engine having a split exhaust system. In one example, a method comprises directing exhaust from a first cylinder group to one or more of a pre-compressor location, a post-compressor location, and an exhaust turbine, and directing exhaust from a second cylinder group to one or more of the pre-compressor location, and the exhaust turbine. Engine efficiency and knock control may be enhanced by directing exhaust gases to different locations based on engine operating conditions.

The invention claimed is: 
     
       1. A method for an engine, comprising:
 during a first condition, directing exhaust from a first cylinder group to a pre-compressor location; 
 directing exhaust from a second cylinder group to an exhaust turbine; and 
 during a second condition, directing exhaust gas from the first cylinder group to a post-compressor location. 
 
     
     
       2. The method of  claim 1 , wherein the first cylinder group and the second cylinder group are mutually exclusive and comprise distinct cylinders. 
     
     
       3. The method of  claim 1 , wherein the second condition includes medium engine load conditions. 
     
     
       4. The method of  claim 3 , further comprising, not directing exhaust from the first cylinder group to either the pre-compressor location or the exhaust turbine. 
     
     
       5. The method of  claim 4 , wherein exhaust from the second cylinder group is directed to the exhaust turbine and not directed to the pre-compressor location. 
     
     
       6. The method of  claim 3 , wherein the post-compressor location includes a location downstream of an intake throttle and upstream of an intake manifold. 
     
     
       7. The method of  claim 1 , wherein the first condition includes high engine load conditions. 
     
     
       8. The method of  claim 7 , wherein directing exhaust to the pre-compressor location includes directing a combination of blowthrough intake air and residual exhaust gases towards an end of an exhaust stroke in each of the first cylinder group and the second cylinder group. 
     
     
       9. The method of  claim 8 , wherein directing the combination of blowthrough intake air and residual exhaust gases towards the end of the exhaust stroke in each of the first cylinder group and the second cylinder group includes providing a positive valve overlap between at least one intake valve and one corresponding exhaust valve of each cylinder in each of the first cylinder group and the second cylinder group. 
     
     
       10. The method of  claim 7 , further comprising not directing exhaust from either the first cylinder group or the second cylinder group to the post-compressor location. 
     
     
       11. The method of  claim 1 , wherein directing exhaust includes selectively opening one or more exhaust valves of each of the first cylinder group and the second cylinder group, and wherein selectively opening includes actuating a cam profile switching device including cam lobes coupled to each of the one or more exhaust valves to vary a timing of opening and a duration of opening of each of the one or more exhaust valves. 
     
     
       12. A method for an engine, comprising:
 during a first condition, recirculating a combination of residual exhaust gases and blowthrough air from a plurality of cylinders of the engine to upstream of a compressor in a first engine cycle; and 
 during a second condition, recirculating all exhaust from only a subset of the plurality of cylinders to downstream of the compressor and delivering exhaust gases from remaining cylinders to an exhaust turbine in a second engine cycle. 
 
     
     
       13. The method of  claim 12 , wherein the first condition includes high engine load conditions and the second condition includes medium engine load conditions. 
     
     
       14. The method of  claim 12 , further comprising during the first condition, delivering a first blowdown portion of exhaust gases to an exhaust turbine, and delivering a second scavenging portion of exhaust gases to an emission control device from the plurality of cylinders. 
     
     
       15. The method of  claim 14 , wherein the first blowdown portion of exhaust gases is delivered to the exhaust turbine via a first exhaust valve of each of the plurality of cylinders, and wherein the second scavenging portion of exhaust gases is delivered to the emission control device via a second exhaust valve of each of the plurality of cylinders. 
     
     
       16. The method of  claim 15 , wherein the combination of residual exhaust gases and blowthrough air is delivered to a location upstream of the compressor via a third exhaust valve of each of the plurality of cylinders. 
     
     
       17. The method of  claim 16 , further comprising during the second condition, delivering a first blowdown portion of exhaust gases to the exhaust turbine, and delivering a second scavenging portion of exhaust gases to an emission control device from the remaining cylinders. 
     
     
       18. A system, comprising:
 an engine having an intake manifold and an exhaust manifold, the exhaust manifold fluidically coupled to an emissions control device; 
 an intake throttle positioned in an intake passage coupled upstream of the intake manifold; 
 a turbocharger including an intake compressor driven by an exhaust turbine; 
 a plurality of cylinders each including a first exhaust valve, a second exhaust valve, and a third exhaust valve; 
 a first exhaust passage fluidically coupling the first exhaust valve directly to only a turbine of the turbocharger; 
 a second exhaust passage fluidically coupling the second exhaust valve directly to only an emissions control device; 
 a third passage fluidically coupling the third exhaust valve directly to only an inlet of the intake compressor; 
 a fourth passage fluidically coupling the third exhaust valve directly to the intake passage, downstream of the intake compressor, downstream of the intake throttle, and upstream of the intake manifold; 
 a first exhaust recirculation valve positioned within the third passage; 
 a second exhaust recirculation valve positioned within the fourth passage; and 
 a cam profile switching system coupled to each of the first exhaust valve, the second exhaust valve, and the third exhaust valve of each of the plurality of cylinders. 
 
     
     
       19. The system of  claim 18 , further comprising a controller with computer readable instructions stored in non-transitory memory for:
 operating the plurality of cylinders in a first mode with the second exhaust valve open and each of the first exhaust valve and the third exhaust valve closed to recirculate all exhaust to the emissions control device; 
 operating the plurality of cylinders in a second mode wherein a subset of the plurality of cylinders is operated with the third exhaust valve open and each of the first exhaust valve and the second exhaust valve closed to recirculate all exhaust to the intake manifold, downstream of the intake compressor and the remaining of the plurality of cylinders are operated with each of the first exhaust valve and the second exhaust valve open and the third exhaust valve closed to deliver portions of exhaust to the exhaust turbine and the emissions control device; and 
 operating the plurality of cylinders in a third mode with each of the first exhaust valve, the second exhaust valve, and the third exhaust valve open to divert portions of exhaust to each of the inlet of the intake compressor, the emissions control device, and the exhaust turbine. 
 
     
     
       20. The system of  claim 19 , wherein the controller includes further instructions for:
 closing each of the first exhaust recirculation valve and the second exhaust recirculation valve when the plurality of cylinders is operating in the first mode; 
 closing the first exhaust recirculation valve and opening the second exhaust recirculation valve when the plurality of cylinders is operating in the second mode; and 
 opening the first exhaust recirculation valve and closing the second exhaust recirculation valve when the plurality of cylinders is operating in the third mode.